The Head-Disk Assembly (HDA) of a disk drive is typically assembled in a clean room environment. To ensure that the head-disk interface remain unencumbered and damage free, it is necessary to reduce the vibrations and drive noise generated by the pivot bearing cartridge of the Head Stack Assembly (HSA). Even low-level friction and noise generated by the pivot bearing may cause damage to the surface of a disk and/or to the read/write head(s), and result in the catastrophic failure of the disk drive. One of the primary causes of pivot bearing friction/noise is pivot bearing damage resulting from unwanted interference with other drive components during the drive assembly process. One source of such interference can be traced to the assembly process, particularly during assembly of the constituent components of the Voice Coil Motor (VCM).
In a modern hard disk drive, and with reference to FIGS. 2, 3 and 4, the HSA 40 is pivotally secured to the base of the drive via a pivot-bearing cartridge 42 so that the read/write transducer(s) 44 at the distal end of the suspension assembly(ies) may be moved over the recording surface(s) of the disk(s) 46. The pivot-bearing cartridge 42 enables the HSA 40 to pivot, and includes a bearing cartridge and a pivot shaft that defines an axis 48 about which the actuator rotates when power is applied to the VCM. The “rotary” or “swing-type” actuator assembly rotates on the pivot bearing cartridge 42 between limited positions, and the coil assembly 52 that extends from one side of the body portion 50 of the actuator body of the HSA 40 is disposed between and interacts with a first permanent magnet 54 mounted to a bottom VCM plate 56 and a second permanent magnet 58 mounted to a top VCM plate 60 to form the VCM formed by the bottom VCM plate 56, the first permanent magnet 54, the coil assembly 52, the second permanent magnet 58 and the top VCM plate 60. In operation, when a driving voltage is applied to the VCM, torque is developed that causes the HSA 40 to pivot about the actuator pivot axis 48 and causes the read/write transducer(s) 44 to sweep radially over the disk(s) 46. Most modern drives use a feedback mechanism so that small changes in applied voltage are operative to position the read/write transducer(s) 44 precisely over the disk(s) 46.
During installation of the VCM, the bottom VCM plate 56 is disposed within the base of the HDA. The HSA is then pivotally fitted onto the base, such that the coil assembly 52 thereof is disposed at least partially over the bottom VCM plate 56. Thereafter, the top VCM plate 60 is lowered over the bottom VCM plate 56, thereby sandwiching the coil assembly 52 between the bottom and top VCM plates 56, 60. During that process, because of the strong permanent magnets 54, 58, a strong magnetic field is established between the first and second permanent magnets, the bottom VCM plate 56 (and its attached magnet 54) has tendency to be attracted towards the top VCM plate 60 as the top VCM plate 60 is lowered down towards the HDA to complete the VCM. As the bottom VCM plate 56 tilts upwards towards the top VCM plate 60, the bottom VCM plate 56's upper surface makes contact with the lower surface of the coil assembly 52 which, in turn, pushes and applies a moment to the actuator body 50, tilting the coil assembly 52 up and the read/write transducers(s) 44 down. This applied moment creates stress on the pivot bearing cartridge (i.e., between the pivot bearings and the pivot shaft), leading to damage of the pivot bearings. The extent of bearing damage is determined by measuring the pivot friction torque. This damage, as alluded to above, may cause unwanted vibration and noise and may even lead to drive failure.
The needs for ever-increasing performance improvement and data storage capacity have been met through increasing the track density and the number of disks in the disk pack and reducing the disk thickness and the spacing between the disks. The increasing number of disks in the disk pack, in particular, has engendered a corresponding increase in the number of actuator arms (four such actuator arms being shown in FIG. 4) on the head stack assembly 40. Moving a more massive HSA 40 while achieving short access times, in turn, requires a stronger magnetic force within the VCM to move the head stack across the disk(s) and to move the heads to and from the ramp load/unload positions within the disk drive assembly. Therefore, there is a need for tools and methods of ever increasing sophistication to overcome the pivot friction damage induced during installation of the top VCM plate 60. Indeed, there is a need to reduce pivot bearing damage caused during installation of the top VCM plate 60 while allowing high performance and high capacity product designs with strong magnetic attraction between the bottom VCM plate 56 and the top VCM plate 60.
FIG. 1 shows a conventional hard disk drive assembly nest 10, used during the manufacture of hard disk drives. Conventionally, the top VCM plate 60 is installed using a conventional top VCM plate gripper assembly 12 mounted on a pneumatic gantry that picks and places the top VCM plate 60 plate into the head disk assembly. Conventionally, the mechanism for holding down the bottom VCM plate 56 is integrated into this top VCM plate gripper assembly 12, as shown in FIG. 5. With reference now to FIGS. 5, 6 and 7, this conventional hold-down mechanism integrated into the top VCM gripper assembly 12 includes hold-down plunger pins 14. The hold-down plunger pins 14 are conventionally spring-loaded by springs within spring cylinders 15. Strong spring forces on the plunger pins 14 are necessary to hold down the bottom VCM plate 56 that has high magnetic attraction towards the top VCM plate 60 during the installation process. The force exerted on the bottom VCM plate 56 by the magnet attached to the top VCM plate 60 is so strong that the long and weak plunger pins 14 frequently break under the strain. In addition, a spring fatigue phenomenon (loss of resiliency of the springs within the spring cylinders 15) renders this conventional spring-loaded plunger pin design inconsistent and ineffective in effectively and consistently holding down the bottom VCM plate 56. In turn, as alluded to above, when the force exerted on the bottom VCM plate 56 exceeds the force applied thereto by the plunger pins 14 of the top VCM plate gripper assembly 12 and causes it to lift from the base, the bottom VCM plate 56 contacts and transfers a moment to the coil assembly 52, thereby tilting the pivot bearing cartridge 42 away from its axis 48 and causing irremediable damage to the constituent bearings thereof and thus to the drive itself. Because of this damage, drive performance and assembly yield suffer. Therefore, the conventional design is not sustainable and has proven to be ineffective in high volume production.
What are needed, therefore, are devices and methods for manufacturing disk drives that do not suffer from the above-described disadvantages.